Micro-fluid ejection devices, such as devices used for ink jet printing and other micro-fluid ejection applications, have become extremely popular for a variety of reasons, including the relative simplicity of their design and lower cost when compared to other types of fluid ejection devices. In basic concept, micro-fluid ejection devices operate by supplying fluid to an ejection head that that may be operable to scan back and forth across a fluid receiving medium such as paper. The ejection head has a matrix of flow features, such as supply channels, fluid ejection chambers, and nozzles. The supply channels feed the fluid to the ejection chambers. The fluid ejection actuators in the ejection chambers impart energy to the fluid that is sufficient to induce the fluid to form a vapor bubble that propels the fluid from the ejection chamber through the nozzle and onto the fluid receiving medium. The element that imparts the energy to the fluid within the ejection chambers may take the form of a resistive heater or a piezoelectric device, for example.
The size and shape of a droplet of fluid that is ejected through the nozzle is determined by a combination of many factors. One factor is an amount of energy that is imparted to the fluid within the ejection chamber. A temperature of a in a vicinity of the ejection chamber tends to play a large role in this factor. In general, ejection chambers that are disposed on a portion of the substrate that is relatively hotter tend to expel fluid droplets that have properties that are different from those fluid droplets that are expelled from ejection chambers that are disposed in a relatively cooler portion of the substrate.
In current micro-fluid ejector designs, an entire ejector array portion of the substrate is heated to a single predetermined temperature. The temperature of the ejector array is typically determined by use of a temperature sensing device that is disposed along the ejector array. The temperature sensor is in communication with a means for heating the ejector array, such as through an external circuit that performs closed loop thermal control of the system. One problem with, this method is that the edges of the ejector array tend to be relatively cooler then the center of tire array. Such thermal gradient along the ejector array may cause fluid ejection problems, such as print detects in the case of ink jet print heads wherein a middle portion of a print swath may have a darker color then edges of the print swath.
One method that has been used to improve fluid ejection non-uniformity is to divide the ejection head into zones and apply separate temperature control to each zone. The zone method allows more heat to be applied to the edges of the ejector array, which helps to keep the edges of the array at the same temperature as the middle of the array. The foregoing design works well for non-jetting modes of operation (such as pre-swath heating) and heating during light fluid coverage of a medium. However, as soon as a swath with a high coverage density is provided, the zone heating design encounters problems. Such high-density swaths tend to cause the micro-fluid ejector substrate to rise above the target temperature. When the ejector array is above the target temperature, the temperature of the substrate can no longer be controlled, because there are no means provided by which heat is removed from the array, other than a natural dissipation of the heat. However, the natural dissipation of heat allows the edges of the ejector array to again become cooler than the middle of the array, which is the very condition that the zone heating was supposed to resolve.
What is needed, therefore, is a system that overcomes problems such as those described above, at least in part.
The above and other needs may be met by a method of controlling a micro fluid ejection device having at least a middle zone with an associated middle zone heater and an edge zone with an associated edge zone heater, where the middle zone is disposed relatively nearer a middle of the micro fluid ejection device substrate and the edge zone is disposed relatively nearer an edge of the micro fluid ejection device substrate. A middle zone epsilon temperature, a middle zone target temperature, a middle zone maximum temperature, an edge zone epsilon temperature, an edge zone target temperature, and an edge zone maximum temperature are specified.
A temperature in the middle zone is sensed to produce a middle zone temperature. Full middle zone power is applied to the middle zone heater when the middle zone temperature is below the middle zone epsilon temperature. Less than the full middle zone power is applied to the middle zone heater when the middle zone temperature is both above the middle zone epsilon temperature and below the middle zone target temperature, where the middle zone power applied is calculated to achieve the middle zone target temperature. No power is applied to the middle zone heater when the middle zone temperature is above the middle zone target temperature.
A temperature in the edge zone is sensed to produce an edge zone temperature. Full edge zone power is applied to the edge zone heater when the edge zone temperature is below the edge zone epsilon temperature. Less than the full edge zone power is applied to the edge zone heater when the edge zone temperature is both above the edge zone epsilon temperature and below the edge zone target temperature, where the edge zone power applied is calculated to achieve the edge zone target temperature. No power is applied to the edge zone heater when the edge zone temperature is above the edge zone maximum temperature.
When the edge zone temperature is both above the edge zone target temperature and below the edge zone maximum temperature, no power is applied to the edge zone heater when the middle zone temperature is below the middle zone target temperature, and less than the full edge power is applied to the edge zone heater when the middle zone temperature is both above the middle zone target temperature and below the middle zone maximum temperature, where the edge zone power applied is calculated to achieve the middle zone temperature.
In various embodiments according to this aspect of the exemplary embodiments, the edge zone epsilon temperature is equal to the middle zone epsilon temperature, the edge zone target temperature is equal to the middle zone target temperature, and the edge zone maximum temperature is equal to the middle zone maximum temperature. In some embodiments the micro fluid ejection device has only two edge zones and only one middle zone, and in other embodiments the micro fluid ejection device has multiple edge zones and multiple middle zones. Also described are a micro fluid ejection device having circuitry that implements the method described above, and a printer with a micro fluid ejection device having circuitry that implements the method.
According to another aspect of the exemplary embodiments there is described a micro field ejection device with at least one middle zone, where the middle zone is disposed relatively nearer a middle of the micro fluid ejection device substrate. A middle zone heater is associated with the middle zone, for heating the middle zone. A middle zone temperature sensor is also associated with the middle zone, for sensing a middle zone temperature. A middle zone controller controls a middle zone power that is applied to the middle zone heater based at least in part on the middle zone temperature. The middle zone controller has set points, including a middle zone epsilon temperature, a middle zone target temperature, and a middle zone maximum temperature. The middle zone controller has circuitry to, (1) apply a full middle zone power to the middle zone heater when the middle zone temperature is below the middle zone epsilon temperature, (2) apply less than the full middle zone power to the middle zone heater when the middle zone temperature is both above the middle zone epsilon temperature and below the middle zone target temperature, where the middle power applied is calculated to achieve the middle zone target temperature, and (3) apply no power to the middle zone heater when the middle zone temperature is above the middle zone target temperature.
The micro fluid ejection device has at least one edge zone, where the edge zone is disposed relatively nearer an edge of the micro fluid ejection device substrate. An edge zone heater is associated with the edge zone, for heating the edge zone. An edge zone temperature sensor is also associated with the edge zone, for sensing an edge zone temperature. An edge zone controller controls an edge zone power that is applied to the edge zone heater, based at least in part on the edge zone temperature. The edge zone controller has set points, including an edge zone epsilon temperature, an edge zone target temperature, and an edge zone maximum temperature. The edge zone controller has circuitry to, (1) apply a full edge zone power to the edge zone hearer when the edge zone temperature is below the edge zone epsilon temperature, (2) apply less than the full edge zone power to the edge zone heater when the edge zone temperature is both above the edge zone epsilon temperature and below the edge zone target temperature, where the edge zone power applied is calculated to achieve the edge zone target temperature, and (3) apply no power to the edge zone heater when the edge zone temperature is above the edge zone maximum temperature.
When the edge zone temperature is both above the edge zone target temperature and below the edge zone maximum temperature, the edge controller can (4) apply no power to the edge zone heater when the middle zone temperature is below the middle zone target temperature, and (5) apply less than the toll edge power to the edge zone heater when the middle zone temperature is both above the middle zone target temperature and below the middle zone maximum temperature, where the edge power applied is calculated to achieve the middle zone temperature.